Gamma-linolenic acid (GLA) is an essential fatty acid in the omega-6 family that is found primarily in plant-based oils. GLA is synthesized from linoleic acid (LA) via the action of the enzyme delta-six desaturase (Δ6-desaturase). The beneficial effects of GLA derive from the fact that GLA serves as the precursor to a number of other essential fatty acids such as arachidonic acid, which is a precursor of prostaglandins and other physiologically important molecules.
Unsaturated fatty acids such as linoleic (C18Δ 9, 12) and α-linolenic (C18Δ 9, 12, 15) acids are essential dietary constituents that cannot be synthesized by vertebrates because while vertebrate cells can introduce double bonds at the Δ 9 position of fatty acids, they cannot introduce additional double bonds between the Δ 9 double bond and the methyl-terminus of the fatty acid chain. Because they are required to synthesize other products, linoleic and α-linolenic acids are essential fatty acids, which are usually obtained from plant sources. LA can be converted by mammals into GLA (C18Δ 6, 9, 12) which can in turn be converted to arachidonic acid (20:4), a critically important fatty acid since it is an essential precursor of most prostaglandins.
The dietary provision of LA, by virtue of its enzymatic conversion to GLA and then into arachidonic acid, could satisfy the dietary need for GLA and arachidonic acid. However, the consumption of fats that are less highly unsaturated, such as LA, has been correlated with health risks such as hypercholesterolemia, atherosclerosis and other clinical disorders which increase susceptibility to coronary disease. In contrast, the consumption of fats that are more highly unsaturated has been associated with decreased blood cholesterol concentration and reduced risk of atherosclerosis. Consumption of the unsaturated fatty acid GLA has been shown to be particularly beneficial. Thus, the consumption of the more unsaturated GLA would be preferred over the consumption of LA. It would thus be desirable to generate additional sources rich in GLA for human consumption.
GLA acts as a precursor for the formation of eicosanoids including prostaglandins. Prostaglandins are vital hormone-like compounds that strengthen cell membranes and serve as cellular signaling molecules. Beneficial effects of GLA have been observed in humans and animals. GLA may help to regulate blood pressure, reduce inflammation and improve immune function. GLA supplementation may benefit a wide range of diseases and conditions including lupus, cancer, allergies, arthritis and ulcerative colitis. GLA may improve the efficacy of drugs used to treat cancer. GLA may help to reduce the symptoms of premenstrual syndrome and menopause; to improve skin health and to treat eczema, acne, rosacea, psoriasis and dandruff; to improve psychiatric and neurological disorders including Alzheimer's disease, Huntington's chorea, multiple sclerosis, attention deficit hyperactivity disorder, depression and Raynaud's phenomenon; to block diabetic neuropathy; to treat cirrhosis of the liver; to improve dry-eye conditions such as Sjögren's syndrome; and to treat cardiovascular disease, osteoporosis, hyperlipidemia and other symptoms associated with aging. Furthermore, GLA has been implicated as a stimulator for the body to burn brown fat. Brown fat is the inner body fat that surrounds vital organs and acts as a fat-burning factory, using calories for heat rather than storing them as white fat. The burning of brown fat is important for the maintenance of ideal body weight. Increased GLA consumption may thus help to stimulate the process of brown fat metabolism.
Existing GLA supplements are typically derived from plant sources that are naturally higher in GLA such as evening primrose oil, black currant oil and borage oil. However, GLA represents a relatively small fraction of the total fatty acids in these natural sources. Only approximately 7-10% (evening primrose), 14-19% (black currant oil) and 20-26% (borage oil) of the fatty acids from these sources are available as GLA. Despite GLA's broad health benefits, its use is currently limited by the high cost and low concentrations of existing GLA supplements. An average adult would need to consume 10 or more capsules of existing GLA supplements to receive its optimal health benefits. It would be useful to have a less expensive, readily available source of oil that was higher in GLA than the naturally occurring specialty oils currently used for GLA supplements. Such a source would allow consumers to receive the optimal health benefits of GLA, while spending less money on supplements and ingesting significantly less total oil and fewer calories.
Safflower is a commercially important agricultural crop. Safflower was first cultivated in the Near East thousands of years ago as a source of dye and other products that could be derived from the plant. Safflower in this century has been utilized as a source of edible oils. Safflower was first introduced to agriculture in the United States in the 1930s as a source of edible oils. Since then, varieties with improved oil content have been developed. Safflower oil primarily comprises the fatty acids palmitic, stearic, oleic and LA. Palmitic (C16:0) and stearic acids (C18:0) are saturated fatty acids; oleic (C18:1) and linoleic (C18:2) are unsaturated fatty acids. However, safflower plants naturally produce only negligible amounts of GLA.
As such, transgenic safflower plants with seeds containing higher levels of GLA than occur naturally would have great utility.